The present invention relates to combined cycle electric power plants and more particularly to improved gas turbine speed/load controls especially useful in backup controllers in combined cycle electric power plants.
In the operation of combined cycle and other gas turbine plants having an automatic control, it is desirable that a backup control be provided for the primary automatic control so as to improve the operating availability of the electric power generating plant. In a coassigned and copending patent application Ser. No. 476,182 filed by R. Yannone et al on June 4, 1974, there is disclosed a backup control for a digital computer automatic control like that disclosed in the previously referenced copending patent application Ser. No. 319,144.
Generally, in the startup of a gas turbine, it is desirable to control the fuel flow to reach synchronous speed rapidly without exceeding equipment design limits and particularly without exceeding blade path or exhaust temperature limits and without entering a surge condition. After synchronization, the fuel flow is controlled to generate demand load where load control is provided or to generate a resulting load where blade path or exhaust temperature limit control is employed.
In startup and load control, it is desirable that backup/primary control transfers be made bumplessly. Further, it is desirable that the backup control be economic yet reliable and sufficiently functional to provide the operator with safe and flexible control over the turbine and the power generating plant either on selection of the backup control mode or on automatic rejection to the backup control mode. In combined cycle plants, it is especially desirable that gas turbine availability be high and that backup control be reliable because of the dependence of the plant on the gas turbine heat supply.
Loft U.S. Pat. No. 3,520,133 shows a feedforward startup control as part of an automatic control of the analog electropneumatic type. The aforementioned Ser. No. 319,114 employs feedforward speed reference generation for a speed feedback control loop in a digital/analog hybrid gas turbine control. In the related steam turbine art, feedforward control has been employed in the forward generation of throttle valve position references as in Eggenberger U.S. Pat. No. 3,097,488 and the forward generation of throttle and governor valve position references as in a copending and coassigned patent application Ser. No. 319,115 entitled "Improved System And Method For Operating A Steam Turbine And An Electric Power Generating Plant" filed by T. Giras et al on Dec. 29, 1972 as a continuation of earlier filed applications, and another copending and coassigned U.S. Pat. application Ser. No. 408,962 entitled "Improved System And Method For Starting, Synchronizing And Operating A Steam Turbine With Digital Computer Control" and filed as a continuation of an earlier filed application by T. Giras et al on Oct. 23, 1973. However, there is no known prior disclosure of the application of feedforward control principles in the provision of reliable, safe, flexible and multi-functional backup control for combined cycle and other gas turbine electric power plants.
The description of prior art herein is made on good faith and no representation is made that any prior art considered is the best pertaining prior art nor that the interpretation placed on its is unrebuttable.